Oxygen reduction reaction

Key takeaways

Oxygen reduction reaction belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Oxygen reduction reaction to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Oxygen reduction reaction from memory before moving on to harder problems.

Reference excerpt

In chemistry, the oxygen reduction reaction refers to the reduction half reaction whereby O2 is reduced to water or hydrogen peroxide. In fuel cells, the reduction to water is preferred because the current is higher. The oxygen reduction reaction is well demonstrated and highly efficient in nature.

Stoichiometry The stoichiometries of the oxygen reduction reaction, which depends on the medium, are shown: 4e− pathway in acid medium: O 2 + 4 e − + 4 H + ⟶ 2 H 2 O {\displaystyle {\ce {O2 + 4 e- + 4H+ -> 2 H2O}}}

2e− pathway in acid medium: O 2 + 2 e − + 2 H + ⟶ H 2 O 2 {\displaystyle {\ce {O2 + 2e- + 2H+ -> H2O2}}}

4e− pathway in alkaline medium: O 2 + 4 e − + 2 H 2 O ⟶ 4 OH − {\displaystyle {\ce {O2 + 4e- + 2H2O -> 4 OH-}}}

2e− pathway in alkaline medium: O 2 + 2 e − + H 2 O ⟶ HO 2 − + OH − {\displaystyle {\ce {O2 + 2e- + H2O -> HO2- + OH-}}}

4e- pathway in solid oxide: O 2 + 4 e − ⟶ 2 O 2 − {\displaystyle {\ce {O2 + 4e- -> 2 O^2-}}}

The 4e− pathway reaction is the cathode reaction in fuel cell especially in proton-exchange membrane fuel cells, alkaline fuel cell and solid oxide fuel cell. While the 2e− pathway reaction is often the side reaction of 4e- pathway or can be used in synthesis of H2O2.

Catalysts

Biocatalysts The oxygen reduction reaction is an essential reaction for aerobic organisms. Such organisms are powered by the heat of combustion of fuel (food) by O2. Rather than combustion, organisms rely on elaborate sequences of electron-transfer reactions, often coupled to proton transfer. The direct reaction of O2 with fuel is precluded by the oxygen reduction reaction, which produces water and adenosine triphosphate. Cytochrome c oxidase affects the oxygen reduction reaction by binding O2 in a heme–Cu complex. In laccase, O2 is engaged and reduced by a four-copper aggregate. Three Cu centers bind O2, and one Cu center functions as an electron donor.

Heterogeneous catalysts In fuel cells, platinum is the most common catalyst. Because platinum is expensive, it is dispersed on a carbon support. Certain facets of platinum are more active than others.

Coordination complexes Detailed mechanistic work results from studies on transition metal dioxygen complexes, which represent models for the initial encounter between O2 and the metal catalyst. Early catalysts for the oxygen reduction reaction were based on cobalt phthalocyanines. Many related coordination complexes have been tested. as the oxygen reduction reaction catalyst and different electrocatalysis performance was achieved by these small molecules. These exciting results trigger further research of the non-noble metal contained small molecules used for the oxygen reduction reaction electrocatalyst. Besides phthalocyanine, porphyrin is also a suitable ligand for metal center to provide N4 part in the M-N4 site. In biosystems, many oxygen related physical chemical reactions are carried by proteins containing the metal-prophyrin unit such as O2 delivery, O2 storage, O2 reduction and H2O2 oxidation.

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Worked examples

Example 1 — a first encounter with Oxygen reduction reaction

Start with the simplest possible case. Write down what Oxygen reduction reaction claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Oxygen reduction reaction before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Oxygen reduction reaction ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Oxygen reduction reaction

In research: Oxygen reduction reaction appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Oxygen reduction reaction in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Oxygen reduction reaction is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cellular respiration, Electrochemistry, Hydrogen peroxide, so understanding it makes those chapters shorter.
In everyday life: Look for Oxygen reduction reaction outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Oxygen reduction reaction in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Oxygen reduction reaction means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Oxygen reduction reaction out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Oxygen reduction reaction in simple terms?

In chemistry, the oxygen reduction reaction refers to the reduction half reaction whereby O2 is reduced to water or hydrogen peroxide. In fuel cells, the reduction to water is preferred because the current is higher.

Why does Oxygen reduction reaction matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Oxygen reduction reaction?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Oxygen reduction reaction.